The device was automatically found by sc_usb_connect(). Instead, expose
a function to find a device from a serial, and let the caller connect to
the device found (if any).
This will allow to list all devices first, then select one device to
connect to.
PR #2974 <https://github.com/Genymobile/scrcpy/pull/2974>
Use it from accept_device() to simplify (at the cost an additional
allocation for each serial, but it is not important).
It will also be useful in other functions in further commits.
PR #2974 <https://github.com/Genymobile/scrcpy/pull/2974>
